The concept of an ADD/DROP Multiplexer (ADM) is implemented by a Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET) technology, and implements ADD and DROP functions of a data service based on a cross-connect matrix of a Time Division Multiplex (TDM) circuit. With the development of the data service, the SDH is developed to a Multi-Service Transport Platform (MSTP) based on the SDH, the data service is adapted to a Virtual Channel (VC) through an adaptation protocol (such as GFP) for being transmitted, but the cross-connect matrix of the MSTP is still implemented based on the TDM technology, and the scheduling of data service is realized by scheduling the matrix using the TDM. However, as the era of all-IP comes, nearly all the data services may be encapsulated and borne by the IP, the data services based on the TDM are gradually reduced. Voice, broadband data, video, and other data services exist in a form of data packets, and each data packet is an independent entity. Therefore, it is outdated to process the ADD and DROP functions of the data service based on the data packet by scheduling the cross-connect matrix of the MSTP that uses the TDM technology based on hard pipes.
As an existing developed technology relevant to the MSTP, a Resilient Packet Ring (RPR) technology is a new type media access control (MAC) layer protocol optimizing the data service transporting on a ring structure, and the detailed description may be obtained with reference to IEEE 802.17. The RPR may be adaptable to various physical layers (for example, SDH, Ethernet, and dense wavelength division multiplexing), and may effectively various service types, such as transport data, voice, and image. The RPR has the economical efficiency, the flexibility, the expandability, and other features of the Ethernet technology, and has a 50 ms fast protection advantage of the SDH ring network. In addition, the RPR has technical advantages such as network topology automatic finding, loop bandwidth sharing, fair assigning, and strict service classifying. The RPR aims to provide a more economical and effective metropolitan area network solution without lowering the network performance and the reliability.
However, the RPR technology has limitations on application, and is a connectionless technology, so the RPR technology cannot completely ensure the Quality of Service (QoS). A distributed fair control algorithm is adopted on Dynamic Bandwidth Assignment (DBA). In the algorithm, each node needs to know all network technologies and process all the algorithms, which is much complicated in implementation.